A highly efficient, reproducible, and scalable approach for exfoliation of MoS2 is critical for utilizing these emerging materials from coatings and composites to printable devices. Additive-free techniques, such as solvent-assisted exfoliation via sonication, are considered to be the most viable approach, where N-methyl-2-pyrrolidone (NMP) is the most effective solvent. However, understanding the mechanism of exfoliation and the key role NMP plays during the process have been elusive and challenges effective improvements in product yield and quality. Here, we report systematic experiments to understand the mechanism of solvent-assisted exfoliation by elucidating the sonolysis chemistries associated with NMP. It is confirmed that in the presence of O2(g) dissolved moisture in NMP plays a critical role during sonication. The higher the moisture content, the more efficient the exfoliation process is. Conversely, when exfoliations are carried out with dried solvents with an inert atmosphere, reaction yields decrease. This is due to redox-active species formed in situ through an autoxidation pathway that converts NMP to N-methyl succinimide by hydroperoxide intermediates. These highly reactive species appear to aid exfoliation by oxidation at reactive edge sites; the charging creates Coulombic repulsion between neighboring sheets that disrupts interlayer basal plane bonding and enables electrostatic stabilization of particles in high-dipole solvents. From these insights, exfoliation in previously reported inactive solvents (e.g., acetonitrile), as well as in the absence of probe sonication, is demonstrated. These findings illustrate that exfoliation of MoS2, and possibly TMD’s in general, can be mediated through understanding the chemistry occurring at the surface–solvent interface.

Mechanical energy harvesters are needed for diverse applications, including self-powered wireless sensors, structural and human health monitoring systems, and the extraction of energy from ocean waves. We report carbon nanotube yarn harvesters that electrochemically convert tensile or torsional mechanical energy into electrical energy without requiring an external bias voltage. Stretching coiled yarns generated 250 watts per kilogram of peak electrical power when cycled up to 30 hertz, as well as up to 41.2 joules per kilogram of electrical energy per mechanical cycle, when normalized to harvester yarn weight. These energy harvesters were used in the ocean to harvest wave energy, combined with thermally driven artificial muscles to convert temperature fluctuations to electrical energy, sewn into textiles for use as self-powered respiration sensors, and used to power a light-emitting diode and to charge a storage capacitor.

Abstract-Many material and biological samples in scientific imaging are characterized by non-local repeating structures. These are studied using scanning electron microscopy and electron tomography. Sparse sampling of individual pixels in a 2D image acquisition geometry, or sparse sampling of projection images with large tilt increments in a tomography experiment, can enable high speed data acquisition and minimize sample damage caused by the electron beam.In this paper, we present an algorithm for electron tomographic reconstruction and sparse image interpolation that exploits the non-local redundancy in images. We adapt a framework, termed plug-and-play (P&P) priors, to solve these imaging problems in a regularized inversion setting. The power of the P&P approach is that it allows a wide array of modern denoising algorithms to be used as a "prior model" for tomography and image interpolation. We also present sufficient mathematical conditions that ensure convergence of the P&P approach, and we use these insights to design a new non-local means denoising algorithm. Finally, we demonstrate that the algorithm produces higher quality reconstructions on both simulated and real electron microscope data, along with improved convergence properties compared to other methods.Index Terms-Plug-and-play, prior modeling, bright field electron tomography, sparse interpolation, non-local means, doublystochastic gradient non-local means, BM3D.

In this work, the suitability of imidazolium-based ionic liquid solvents is investigated for the dissolution and regeneration of silkworm (Bombyx mori) silk. Within an ionic liquid the anion plays a larger role in dictating the ultimate solubility of the silk. The dissolution of the silk in the ionic liquid is confirmed using wide-angle X-ray scattering. The dissolved silk is also processed into 100 mum-thick, two-dimensional films, and the structure of these films is examined. The rinse solvent, acetonitrile or methanol, has a profound impact on both the topography of the films and the secondary structure of the silk protein. The image depicts a silkworm cocoon dissolved in 1-butyl-3-methylimidazolium chloride and then regenerated as a film with birefringence.

Gold nanorods (Au NRs) are the archetype of a nanoantenna, enabling the directional capture, routing, and concentration of electromagnetic fields at the nanoscale. Solution-based synthesis methods afford advantages relative to top-down fabrication but are challenged by insufficient precision of structure, presence of byproducts, limited tunability of architecture, and device integration. This is due in part to an inadequate understanding of the early stages of Au NR growth. Here, using phase transfer via ligand exchange with monothiolated polystyrene, we experimentally demonstrate the complete evolution of seed-mediated Au NR growth in hexadecyltrimethylammonium bromide (CTAB) solution. Au NR size and shape progress from slender spherocylinders at short reaction times to rods with a dumbbell profile, flattened end facets, and octagonal prismatic structures at later stages. These evolve from a single mechanism and reflect the majority of reported Au NR morphologies, albeit reflecting different stages. Additionally, the fraction of nonrod impurities in a reaction is related to the initial distribution of the structure of the seed particles. Overall, the observations of early and intermediate stage growth are consistent with the formation of a surfactant bilayer on different crystal facets at different growth stages due to a fine balance between kinetic and thermodynamic factors.